CXCR4 and neoplasm: CXCR4 is the most common chemokine receptor mediating liver metastases initiation and CXCR4/CXCL12 participate in extravasation of tumor cells within the liver in a rat model.126 Cytokines also stimulate macrophages to produce TNFα, which up-regulates E-selectin expression, and therefore promotes cell adherence to endothelium.